Function of the circulatory system in molluscs?

The mollusk circulatory system uses blood to transport both oxygen from the respiratory system to the organs and tissues of the animal, and waste carbon dioxide from these tissues back to the respiratory system. This system is much more efficient than the simple diffusion between tissues and the environment that occurs in simpler invertebrates such as roundworms. The mollusk circulatory system uses the heart to pump blood through the body. The heart pumps blood through the blood vessels that run from the gills into the body cavity.